Radio communication devices, such as pagers, typically receive and decode radio frequency (RF) signals to recover information contained therein. In many conventional radio communication devices, a received signal is first converted from the radio frequency at which it is received to baseband, subsequent to which digital data is recovered from the signal. The data is then processed by decoding circuitry, such as a microcomputer, which decodes the included information.
In order to recover the digital data from an incoming signal, the microcomputer generally directs tracking circuitry included within the radio communication device to track the incoming signal for a predetermined amount of time to acquire peak and valley values, i.e., high and low voltage values, of the signal. Once the incoming signal has stabilized and the peak and valley values have been acquired, they are stored and provided to a threshold detector for computation of a center threshold between the values. The threshold detector utilizes the peak and valley values and the center threshold to generate from the incoming signal a stream of digital data for provision to the microcomputer or other decoding circuitry.
Conventionally, the tracking circuitry is set at a predetermined acquisition rate which determines the response time in which changing peak and valley values can be acquired. This acquisition rate is usually set to a relatively slow rate such that small deviations in a desired signal, such as those caused by noise on the channel, do not cause the desired, stable values to fluctuate and thus cause errors in the data recovery process. However, a slow acquisition rate, although necessary for accurate data recovery, can sometimes cause problems when the radio communication device is in a noisy or fading environment.
When no signal is present on the channel, or when a very noisy signal is present, the peak and valley values present on the channel can fluctuate rapidly and may be very unstable. Additionally, the values present on the noisy channel may be well above or below the true peak and valley values of the desired signal. Because of the fairly slow acquisition rate, the tracking circuitry may be unable to track the peak and valley values of the noisy signals as quickly as they are fluctuating. Therefore, when the desired signal is received, the tracking circuitry may not be able to immediately acquire the stable values.
By way of example, when the fluctuating peak and valley values of a noisy signal drop to more stable values indicative of a desired signal, the tracking circuitry requires a response time, which depends upon the predetermined acquisition rate, to decrement or increment internal counters from the undesired values to the stable values of the desired signal. As a result, during the response time of the tracking circuitry, data included in a desired signal may be "missed" until the tracking circuitry has acquired the correct peak and valley values of the desired signal.
Thus, what is needed is a radio communication device having tracking circuitry which is able to rapidly acquire changing peak and valley values. Additionally, small deviations in the peak and valley values of a desired signal should not cause stored peak and valley values to fluctuate.